fix mocked assert

cloudside/tests/test_asos.py

@@ -143,7 +143,7 @@ def test_fetch_files(ftp_login, ftp_retr):
         )
         assert isinstance(raw_paths, filter)
         assert all([(isinstance(rp, pathlib.Path) or (rp is None)) for rp in raw_paths])
-        assert ftp_login.called_once_with("[email protected]")
+        ftp_login.assert_called_once_with("[email protected]")
         assert ftp_retr.call_count == 5